The invention relates to a stacking device for stacking articles or article groups on top of each other, the articles being supplied to that stacking device in a single stream and at a common first level, the device comprising elements which are moveable substantially parallel to the article track, which are adapted to receive one or more articles each time, and which are designed to move through a first track section and a second downstream track section, wherein in the first track section, articles are to be received and in the second track section, the articles are to be delivered at a subsequent level different to that of said first level, and means, in or beyond the second track section, for positioning a group of articles, successively located at various levels, substantially on top of each other.
A similar stacking device is known from the German "Offenlegungsschrift" 3827063. The stacking device described in it makes use of sets of moveable plateaus, installed opposite each other on both sides of the article stream and parallel to the article stream, which receive an article between them each time. The elements move in a loop lying in a plane substantially parallel to the article stream. While a set of elements with an article in between moves downstream, the set is also raised to a specific level. For a number of consecutive sets, where the number corresponds to the number of articles in the stack to be taken up, each next set is raised to a higher level. At the same time, the speed of motion of that number of sets decreases in such a way that the sets at different levels move above each other. Following this, each article is deposited on the article underneath it, and the undermost article onto a further conveyor belt. An article stack is thus built, while maintaining a forward movement during the formation of the stack.
Another stacking device is known from the European patent specification 0312490, wherein successively supplied articles are deposited on a single plateau, the level of which after receiving the article is lowered approximately the height of the article. Each following article falls thus automatically on top of the preceding article, and when the stack is complete, this is removed from the plateau and is moved downstream. For creating a stack with this known device, it is thus a necessity that all articles are slowed down to a standstill, after which the stack is again accelerated. Consequently, this known device is little suited to high speed processing of articles delivered in one stream.
Furthermore, U.S. Pat. No. 4,413,462 specifies supplying articles in two parallel streams and at the same level, after which the one stream is then lifted above the other stream, to bring the two parallel streams immediately above each other. Next, with the aid of a driver, two articles are "swept" on top of each other, so that, consequently, at the end of the upper level they are dropped on top of each other. Although no important deceleration and/or acceleration of the articles occurs for the creation of the stack, the disadvantage is that there have to be two article streams to be created next to each other, and following that those streams must be brought above each other. A stacking device which is suited for such operation is consequently complex, and, for efficient operation, only suitable for stacks of only two articles.
EP-A-0 521 428 concerns another stacking device, using a large vertically disposed rotating stacking wheel, having circumferential recesses of different depth. The articles are supplied at one level, and are dropped subsequently in a corresponding recess. By rotating the wheel, the articles in the respective recess are moved downstream and are transferred to fixed slide plates at levels corresponding to the level of the bottom of the respective recess at the position of transfer. This device demands a stacking wheel of large dimensions, with high demands for structural provisions, space, drive systems, maintenance as well as costs. Speed control of the stacking wheel demands high decelerating and accelerating forces, such that the device is less suitable for high speeds of operation. The recesses give rise to problems if the article dimension will be changed. Modification of the device to accommodate another amount of articles in one stack, seems cumbersome, requiring replacement of the stacking wheel. In fact, the recesses are only suitable for relatively elongate articles, supplied cross-wise. Since the chain 3 (refer to FIG. 3) extends within the stacking wheel (for which reason said wheel is divided), it is easily contaminated by substances from the articles, such as if the articles are baked (crumbly) articles. The contaminations give rise to increased failures, while the locations at and around the stacking wheel are difficult to clean. Furthermore, the chain 3 has to protrude into the stacking wheel to a great extent, giving rise to guidance problems with respect to said chain 3 as well as the drivers 4, leading to increased wear and/or costs. There is a chance of damage to the articles, especially at high operational speeds, since they fall down into a recess, which itself is moving upwards at that same moment.
EP-A-0 260 363 shows a stacking device for providing a two-article stack. Articles are fed in one stream towards a chain with spaced bodies protruding from the face of a conveyor belt. Articles are alternatively picked up by the upper face of the bodies, or the upper face of the conveyor belt at the region where the upper part of said conveyor belt is upwardly inclined from below the level of the article stream in a downstream direction. The upper article resting on the body is first decelerated by slide plates at both sides of the body bearing the articles in the same horizontal plane, such that the downstream lower article resting on the conveyor belt will move until immediately below the upper article. A downstream driver subsequently accelerates the upper article to move together with the lower article, and to shift it from the slide plate on to the top of the lower article. This device demands a conveyor belt with lifting bodies running in the vertical plane, with the lower part below the upper part, which can therefor easily become contaminated. Furthermore, this known device is less suitable for high operational speeds, since the articles are lifted by the rising bodies from beneath, possibly leading to upward hitting of the articles, which then can fall from the body or can be damaged. Also, the alignment of the upper face of the bodies and the upper face of the slide plate for deceleration of the upper article needs extreme accuracy. At high operating speeds, when the conveyor belt carrying the bodies is vibrating up and down, the upper articles are alternately carried by the slide plates and the body, possibly giving rise to failures.